Computers have I/O (Input/Output) buses used to expand functions. Examples of a standard I/O bus include a PCI (Peripheral Component Interconnect) bus and a PCIe (PCI Express) bus. To such a computer, a PCI device such as a NIC (Network Interface Card) can be coupled during operation of the computer. Attaching and detaching of the PCI device during operation of the computer is referred to as “hot-swap”.
For example, when the hot-swap is performed on a computer using PCI devices which are compatible with PCI buses, the computer assigns identification numbers unique to the PCI devices coupled to the computer. Each of the identification numbers includes a bus number used to identify a bus configuration of a PCI bus and a device number used to identify a device coupled to a corresponding bus. The computer recognizes the connection relationship with the PCI devices using the identification numbers having bus numbers and device numbers.
The computer has a plurality of I/O slots. The computer is coupled to the PCI devices through the I/O slots. In the computer, a plurality of PCI devices may be coupled to a single I/O slot. The computer sets ranges of the identification numbers settable to the I/O slots in advance. In the identification numbers settable to the I/O slots, ranges of the bus numbers are limited. When the identification numbers set to the I/O slots include an unused bus number, the computer recognizes a PCI device which is newly coupled to one of the I/O slots.
As a technique of connecting a plurality of PCI devices to a single I/O slot, a switch apparatus has been proposed. The switch apparatus includes an upstream bridge and a plurality of downstream bridges. The upstream bridge is coupled to one of the I/O slots of the computer. The downstream bridges are coupled to individual PCI devices. Using the switch apparatus, a plurality of PCI devices are coupled to a single I/O slot by switching connections between the upstream bridge and the downstream bridges from one to another. The computer assigns identification numbers having different bus numbers to the PCI devices coupled to the downstream bridges. Japanese Laid-open Patent Publication No. 2007-226653 and Japanese Laid-open Patent Publication No. 2009-169842 disclose techniques of connecting a plurality of PCI devices to a computer.
When a switch apparatus to which a plurality of devices are coupled by hot-swap is coupled to a computer, the number of coupled devices may exceed a range of identification numbers assigned to I/O slots of the computer. The computer is not capable of recognizing devices having identification numbers which are out of the range of the assigned identification numbers.